DOCSLIB.ORG

First Firm Spectral Classification of an Early-B Pre-Main-Sequence Star: B275 in M

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
First Firm Spectral Classification of an Early-B Pre-Main-Sequence Star: B275 in M A&A 536, L1 (2011) Astronomy DOI: 10.1051/0004-6361/201118089 & c ESO 2011 Astrophysics Letter to the Editor First firm spectral classification of an early-B pre-main-sequence star: B275 in M 17 B. B. Ochsendorf1, L. E. Ellerbroek1, R. Chini2,3,O.E.Hartoog1,V.Hoffmeister2,L.B.F.M.Waters4,1, and L. Kaper1 1 Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE Amsterdam, The Netherlands e-mail: [email protected]; [email protected] 2 Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany 3 Instituto de Astronomía, Universidad Católica del Norte, Antofagasta, Chile 4 SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands Received 14 September 2011 / Accepted 25 October 2011 ABSTRACT The optical to near-infrared (300−2500 nm) spectrum of the candidate massive young stellar object (YSO) B275, embedded in the star-forming region M 17, has been observed with X-shooter on the ESO Very Large Telescope. The spectrum includes both photospheric absorption lines and emission features (H and Ca ii triplet emission lines, 1st and 2nd overtone CO bandhead emission), as well as an infrared excess indicating the presence of a (flaring) circumstellar disk. The strongest emission lines are double-peaked with a peak separation ranging between 70 and 105 km s−1, and they provide information on the physical structure of the disk. The underlying photospheric spectrum is classified as B6−B7, which is significantly cooler than a previous estimate based on modeling of the spectral energy distribution. This discrepancy is solved by allowing for a larger stellar radius (i.e. a bloated star) and thus positioning the star above the main sequence. This constitutes the first firm spectral classification of an early-B pre-main-sequence (PMS) star. We discuss the position of B275 in the Hertzsprung-Russell diagram in terms of PMS evolution. Although the position −5 −1 is consistent with PMS tracks of heavily accreting protostars (M˙ acc ∼> 10 M yr ), the fact that the photosphere of the object is detectable suggests that the current mass-accretion rate is not very high. Key words. stars: formation – stars: pre-main-sequence – stars: massive – stars: variables: T Tauri, Herbig Ae/Be 1. Introduction Infrared surveys have revealed several hundred candidate massive YSOs, based on luminosity arguments (e.g., Urquhart Observational and theoretical evidence is accumulating that the et al. 2011). A (K-band) spectrum has been obtained for only formation process of massive stars is through disk accretion, afewofthese(Hanson et al. 1997, 2002; Bik et al. 2006), similar to low-mass stars. This persists despite the strong ra- and they show a red continuum, likely due to hot dust, and an diation pressure and ionizing power produced by the massive emission-line spectrum that includes Brγ and, often, CO 2.3 μm young stellar object (YSO) that may reverse the accretion flow bandhead emission. The latter emission can be modeled as being and prevent matter from accreting onto the forming star (e.g., produced by a Keplerian rotating disk surrounding the young, Keto et al. 2006; Krumholz et al. 2009). Given the short main- potentially massive star (Bik & Thi 2004; Blum et al. 2004; sequence lifetime of massive stars, the mass accretion rate must −3 −1 Wheelwright et al. 2010). be high (up to ∼10 M yr , Hosokawa et al. 2010) to ensure that the star is not leaving the main sequence before the accretion As massive stars show most spectral features in the UV and process has finished. optical ranges, the study of their photospheric properties would Evidence of accretion must come from the detection of cir- strongly benefit from extending the spectral coverage as far to cumstellar disks, and possibly bipolar jets, as observed around the blue as possible. Obviously, extinction by the surrounding forming low-mass stars (e.g., Appenzeller & Mundt 1989). gas and dust makes this an observational challenge. Only in rare Disks and outflows around massive YSO candidates are being cases have spectra of candidate massive YSOs been obtained at reported (e.g., Chini et al. 2004; Kraus et al. 2010; Ellerbroek optical wavelengths. Hanson et al. (1997) obtained optical and et al. 2011), but the physical properties of the forming massive near-infrared spectra of candidate massive YSOs in M 17, one stars remain uncertain. The mass of the central object has to be of the most massive nearby star-forming regions in the Galaxy estimated from the emerging flux, and the direct detection of the (Hoffmeister et al. 2008; Broos et al. 2007; Povich et al. 2009). photospheric spectrum turns out to be very difficult at this early For the “normal” OB stars Hanson et al. (1997) found a good stage of evolution (e.g., Testi et al. 2010). correspondence between the optical and K-band spectra, but the massive YSO optical spectra remained inconclusive. For four Based on observations performed with the ESO Very Large massive YSO candidates, they registered the optical spectrum Telescope on Cerro Paranal, Chile, as part of the X-shooter Science from 400 to 480 nm, indicating a high mass and luminosity. The Verification program 60.A-9402(A). blue spectrum of the strong CO emission source B275 showed Article published by EDP Sciences L1, page 1 of 4 A&A 536, L1 (2011) H HeI H HeI HeI DIB HeI MgII H H HeI SiII H 4 CaII CII 3.5 c B2V + 3 B3V ux fl B5V 3.0 2 B275 H norm. B7V 1 B8V 2.5 CaII 849.8 380 400 420 440 460 (nm) CaII 854.2 2.0 1.5 norm. flux + c CaII 866.2 1.4 1.3 1.5 OI 844.6 1.2 (4-2) (5-2) (2-0) (3-0) 1.1 (3-1) (4-1) (5-3) (6-3) [OI] 630.0 1.0 1.0 0.9 0 5 10 15 -400 -200 0 200 400 Fig. 1. Top left: the blue spectrum of B275 in M 17 shown next to B main-sequence-star spectra (Gray & Corbally 2009). Bottom left:the 1st and 2nd overtone CO emission bands. Zero velocity corresponds to the first component in the series (at 2294 and 1558 nm, respectively). Right: a sample of the emission line profiles in the spectrum of B275. The Ca ii triplet lines and O i 845 nm are superposed on hydrogen Paschen series absorption lines. The flux of the Hα line is scaled down by a factor 5; the structure near the peak is a remnant of the nebular-line subtraction. no definite photospheric features other than hydrogen, so that 3. Results the nature of this source remained uncertain. The spectral en- ergy distribution (SED), though, indicated spectral type late-O In the following we present the results for the accurate classifica- or early B, at an adopted distance of 1.3 kpc. We set out to tion of the photospheric spectrum, analyze the interstellar spec- exploit the high efficiency and broad wavelength coverage of trum to determine the extinction, model the SED using the flux- the new medium-resolution spectrograph X-shooter on the ESO calibrated X-shooter spectrum, and describe the emission-line Very Large Telescope (VLT) to (i) detect the photospheric spec- spectrum produced by the circumstellar disk. trum of B275 in M 17; (ii) determine its effective temperature in order to place the candidate massive YSO unambiguously onto 3.1. Spectral classification recent evolutionary tracks; and (iii) search for ongoing accretion activity and investigate the structure of the disk. Hydrogen absorption lines were detected by Hanson et al. (1997) in the blue spectrum of B275, but do not allow for an accu- rate spectral classification. As shown in Fig. 1, a number of 2. VLT/X-shooter observations of B275 helium and metal lines can be used to classify the photo- VLT/X-shooter spectra were obtained of the massive YSO B275 spheric spectrum. The He i 400.9 nm and C ii 426.7 nm, in M 17 (CEN 24, RA(2000.0) = 18h20m25s.13, Dec(2000.0) = prominent down to spectral type B3, are very weak. The −16◦1024. 56, V = 15.55 mag, K = 8.05 mag, Chinietal. He i 447.1 nm/Mg ii 448.1 nm ratio is a useful spectral indicator 1980; Skrutskie et al. 2006) on August 11, 2009 at 03h20 UT, for mid- to late-B stars (Gray & Corbally 2009) as the neutral during the first science verification run (PI Chini). The observa- helium line disappears towards lower temperature (A0) and the tions in the UVB arm (300−600 nm) were binned (2 pixels) in magnesium line strengthens. When also considering another line the wavelength direction in order to increase the signal-to-noise ratio, Si ii 412.8 nm/He i 448.1 nm, the spectral type becomes B6 ratio of this part of the spectrum, while still oversampling the (±one subtype). resolution element. The 1.6 slit was used resulting in resolving The spectral type and luminosity class of B275 are further power R = 3300. For the VIS (550−1000 nm) and the NIR arm constrained by comparison of the observed H i and He i line pro- (1000−2500 nm) a 0.9 slit was used (R = 8800 and 5600, re- files (as well as the shape of the SED, see Sect. 3.3), to model spectively). The total exposure time was 45 min, resulting in profiles produced with FASTWIND (Puls et al. 2005). This code a typical signal-to-noise ratio of 70. For more details on the calculates non-LTE line-blanketed stellar atmosphere models X-shooter instrument and its performance, see D’Odorico et al.
Load more

Recommended publications
  • Spectroscopic Analysis of Accretion/Ejection Signatures in the Herbig Ae/Be Stars HD 261941 and V590 Mon T Moura, S
    Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon T Moura, S. Alencar, A. Sousa, E. Alecian, Y. Lebreton To cite this version: T Moura, S. Alencar, A. Sousa, E. Alecian, Y. Lebreton. Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2020, 494 (3), pp.3512-3535. 10.1093/mnras/staa695. hal-02523038 HAL Id: hal-02523038 https://hal.archives-ouvertes.fr/hal-02523038 Submitted on 16 May 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. MNRAS 000,1–24 (2019) Preprint 27 February 2020 Compiled using MNRAS LATEX style file v3.0 Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon T. Moura1?, S. H. P. Alencar1, A. P. Sousa1;2, E. Alecian2, Y. Lebreton3;4 1Universidade Federal de Minas Gerais, Departamento de Física, Av. Antônio Carlos 6627, 31270-901, Brazil 2Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France 3LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ.
    [Show full text]
  • Plotting Variable Stars on the H-R Diagram Activity
    Pulsating Variable Stars and the Hertzsprung-Russell Diagram The Hertzsprung-Russell (H-R) Diagram: The H-R diagram is an important astronomical tool for understanding how stars evolve over time. Stellar evolution can not be studied by observing individual stars as most changes occur over millions and billions of years. Astrophysicists observe numerous stars at various stages in their evolutionary history to determine their changing properties and probable evolutionary tracks across the H-R diagram. The H-R diagram is a scatter graph of stars. When the absolute magnitude (MV) – intrinsic brightness – of stars is plotted against their surface temperature (stellar classification) the stars are not randomly distributed on the graph but are mostly restricted to a few well-defined regions. The stars within the same regions share a common set of characteristics. As the physical characteristics of a star change over its evolutionary history, its position on the H-R diagram The H-R Diagram changes also – so the H-R diagram can also be thought of as a graphical plot of stellar evolution. From the location of a star on the diagram, its luminosity, spectral type, color, temperature, mass, age, chemical composition and evolutionary history are known. Most stars are classified by surface temperature (spectral type) from hottest to coolest as follows: O B A F G K M. These categories are further subdivided into subclasses from hottest (0) to coolest (9). The hottest B stars are B0 and the coolest are B9, followed by spectral type A0. Each major spectral classification is characterized by its own unique spectra.
    [Show full text]
  • Stellar Magnetic Activity – Star-Planet Interactions
    EPJ Web of Conferences 101, 005 02 (2015) DOI: 10.1051/epjconf/2015101005 02 C Owned by the authors, published by EDP Sciences, 2015 Stellar magnetic activity – Star-Planet Interactions Poppenhaeger, K.1,2,a 1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambrigde, MA 02138, USA 2 NASA Sagan Fellow Abstract. Stellar magnetic activity is an important factor in the formation and evolution of exoplanets. Magnetic phenomena like stellar flares, coronal mass ejections, and high- energy emission affect the exoplanetary atmosphere and its mass loss over time. One major question is whether the magnetic evolution of exoplanet host stars is the same as for stars without planets; tidal and magnetic interactions of a star and its close-in planets may play a role in this. Stellar magnetic activity also shapes our ability to detect exoplanets with different methods in the first place, and therefore we need to understand it properly to derive an accurate estimate of the existing exoplanet population. I will review recent theoretical and observational results, as well as outline some avenues for future progress. 1 Introduction Stellar magnetic activity is an ubiquitous phenomenon in cool stars. These stars operate a magnetic dynamo that is fueled by stellar rotation and produces highly structured magnetic fields; in the case of stars with a radiative core and a convective outer envelope (spectral type mid-F to early-M), this is an αΩ dynamo, while fully convective stars (mid-M and later) operate a different kind of dynamo, possibly a turbulent or α2 dynamo. These magnetic fields manifest themselves observationally in a variety of phenomena.
    [Show full text]
  • • Classifying Stars: HR Diagram • Luminosity, Radius, and Temperature • “Vogt-Russell” Theorem • Main Sequence • Evolution on the HR Diagram
    Stars • Classifying stars: HR diagram • Luminosity, radius, and temperature • “Vogt-Russell” theorem • Main sequence • Evolution on the HR diagram Classifying stars • We now have two properties of stars that we can measure: – Luminosity – Color/surface temperature • Using these two characteristics has proved extraordinarily effective in understanding the properties of stars – the Hertzsprung- Russell (HR) diagram If we plot lots of stars on the HR diagram, they fall into groups These groups indicate types of stars, or stages in the evolution of stars Luminosity classes • Class Ia,b : Supergiant • Class II: Bright giant • Class III: Giant • Class IV: Sub-giant • Class V: Dwarf The Sun is a G2 V star Luminosity versus radius and temperature A B R = R R = 2 RSun Sun T = T T = TSun Sun Which star is more luminous? Luminosity versus radius and temperature A B R = R R = 2 RSun Sun T = T T = TSun Sun • Each cm2 of each surface emits the same amount of radiation. • The larger stars emits more radiation because it has a larger surface. It emits 4 times as much radiation. Luminosity versus radius and temperature A1 B R = RSun R = RSun T = TSun T = 2TSun Which star is more luminous? The hotter star is more luminous. Luminosity varies as T4 (Stefan-Boltzmann Law) Luminosity Law 2 4 LA = RATA 2 4 LB RBTB 1 2 If star A is 2 times as hot as star B, and the same radius, then it will be 24 = 16 times as luminous. From a star's luminosity and temperature, we can calculate the radius.
    [Show full text]
  • The Hr Diagram for Late-Type Nearby Stars
    379 THE H-R DIAGRAM FOR LATE-TYPE NEARBY STARS AS A FUNCTION OF HELIUM CONTENT AND METALLICITY 1 2 3 2 1 1 Y. Lebreton , M.-N. Perrin ,J.Fernandes ,R.Cayrel ,G.Cayrel de Strob el , A. Baglin 1 Observatoire de Paris, Place J. Janssen - 92195 Meudon Cedex, France 2 Observatoire de Paris, 61 Avenue de l'Observatoire - 75014 Paris, France 3 Observat orio Astron omico da Universidade de Coimbra, 3040 Coimbra, Portugal Key words: Galaxy: solar neighb ourho o d; stars: ABSTRACT abundances; stars: low-mass; stars: HR diagram; Galaxy: abundances. Recent theoretical stellar mo dels are used to discuss the helium abundance of a numberoflow-mass stars for which the p osition in the Hertzsprung-Russell di- 1. INTRODUCTION agram and the metallicity are known with high accu- racy. The knowledge of the initial helium abundance of Hipparcos has provided very high quality parallaxes stars b orn in di erent sites with di erent metallicities of a sample of a hundred disk stars, of typeFtoK,lo- is of great imp ortance for many astrophysical stud- cated in the solar neighb ourho o d. Among these stars ies. The lifetime of a star and its internal structure we have carefully selected those for which detailed very much dep end on its initial helium content and sp ectroscopic analysis has provided e ective temp er- this has imp ortant consequences not only for stellar ature and [Fe/H] ratio with a high accuracy. astrophysics but also in cosmology or in studies of the chemical evolution of galaxies. Wehave calculated evolved stellar mo dels and their Direct measurement of the helium abundance in the asso ciated iso chrones in a large range of mass, for photosphere of a low mass star cannot b e made since several values of the metallicity and of the helium there are no helium lines in the sp ectra.
    [Show full text]
  • Evolution, Mass Loss and Variability of Low and Intermediate-Mass Stars What Are Low and Intermediate Mass Stars?
    Evolution, Mass Loss and Variability of Low and Intermediate-Mass Stars What are low and intermediate mass stars? Defined by properties of late stellar evolutionary stages Intermediate mass stars: ~1.9 < M/Msun < ~7 Develop electron-degenerate cores after core helium burning and ascending the red giant branch for the second time i.e. on the Asymptotic Giant Branch (AGB). AGB Low mass stars: M/Msun < ~1.9 Develop electron-degenerate cores on leaving RGB the main-sequence and ascending the red giant branch for the first time i.e. on the Red Giant Branch (RGB). Maeder & Meynet 1989 Stages in the evolution of low and intermediate-mass stars These spikes are real The AGB Surface enrichment Pulsation Mass loss The RGB Surface enrichment RGB Pulsation Mass loss About 108 years spent here Most time spent on the main-sequence burning H in the core (~1010 years) Low mass stars: M < ~1.9 Msun Intermediate mass stars: Wood, P. R.,2007, ASP Conference Series, 374, 47 ~1.9 < M/Msun < ~7 Stellar evolution and surface enrichment The Red giant Branch (RGB) zHydrogen burns in a shell around an electron-degenerate He core, star evolves to higher luminosity. zFirst dredge-up occurs: The convection in the envelope moves in when the stars is near the bottom of the RGB and "dredges up" material that has been through partial hydrogen burning by the CNO cycle and pp chains. From John Lattanzio But there's more: extra-mixing What's the evidence? Various abundances and isotopic ratios vary continuously up the RGB. This is not predicted by a single first dredge-up alone.
    [Show full text]
  • Multicolor Photometric Behavior of the Young Stellar Object V1704 Cygni
    Multicolor photometric behavior of the young stellar object V1704 Cygni Sunay Ibryamov1, Evgeni Semkov2, Stoyanka Peneva2, U˘gur Karadeniz3 1 Department of Physics and Astronomy, University of Shumen, 115, Universitetska Str., 9700 Shumen, Bulgaria 2 Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria 3 Department of Physics, Izmir Institute of Technology, Urla, 35430 Izmir, Turkey [email protected] (Submitted on 22.01.2018. Accepted on 20.02.2018) Abstract. Results from BV RI photometric observations of the pre-main sequence star V1704 Cyg collected during the time period from August 2010 to December 2017 are presented. The star is located in the star-forming HII region IC 5070 and it exhibits photometric variability in all optical passbands. After analyzing the obtained data, V1704 Cyg is classified as a classical T Tauri star. Key words: stars: pre-main sequence, stars: variables: T Tauri, star: individual: (V1704 Cyg) 1. Introduction One of the most frequent types of pre-main sequence (PMS) stars are the low-mass (M ≤ 2M⊙) T Tauri stars (TTSs). The first study of the TTSs as a separate class of variables with the prototype star T Tau was made by Joy (1945). These stars show irregular photometric variability and emission spectra. TTSs are divided into two sub-classes: classical T Tauri stars (CTTSs) still actively accreting from their massive circumstellar disks and the weak- line T Tauri stars (WTTSs) without evidence of disk accretion (M´enard
    [Show full text]
  • Spectral Classification and HR Diagram of Pre-Main Sequence Stars in NGC 6530
    A&A 546, A9 (2012) Astronomy DOI: 10.1051/0004-6361/201219853 & c ESO 2012 Astrophysics Spectral classification and HR diagram of pre-main sequence stars in NGC 6530,, L. Prisinzano, G. Micela, S. Sciortino, L. Affer, and F. Damiani INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, Italy 1, 90134 Palermo, Italy e-mail: [email protected] Received 20 June 2012 / Accepted 3 August 2012 ABSTRACT Context. Mechanisms involved in the star formation process and in particular the duration of the different phases of the cloud contrac- tion are not yet fully understood. Photometric data alone suggest that objects coexist in the young cluster NGC 6530 with ages from ∼1 Myr up to 10 Myr. Aims. We want to derive accurate stellar parameters and, in particular, stellar ages to be able to constrain a possible age spread in the star-forming region NGC 6530. Methods. We used low-resolution spectra taken with VLT/VIMOS and literature spectra of standard stars to derive spectral types of a subsample of 94 candidate members of this cluster. Results. We assign spectral types to 86 of the 88 confirmed cluster members and derive individual reddenings. Our data are better fitted by the anomalous reddening law with RV = 5. We confirm the presence of strong differential reddening in this region. We derive fundamental stellar parameters, such as effective temperatures, photospheric colors, luminosities, masses, and ages for 78 members, while for the remaining 8 YSOs we cannot determine the interstellar absorption, since they are likely accretors, and their V − I colors are bluer than their intrinsic colors.
    [Show full text]
  • Chapter 11 SOLAR RADIO EMISSION W
    Chapter 11 SOLAR RADIO EMISSION W. R. Barron E. W. Cliver J. P. Cronin D. A. Guidice Since the first detection of solar radio noise in 1942, If the frequency f is in cycles per second, the wavelength radio observations of the sun have contributed significantly X in meters, the temperature T in degrees Kelvin, the ve- to our evolving understanding of solar structure and pro- locity of light c in meters per second, and Boltzmann's cesses. The now classic texts of Zheleznyakov [1964] and constant k in joules per degree Kelvin, then Bf is in W Kundu [1965] summarized the first two decades of solar m 2Hz 1sr1. Values of temperatures Tb calculated from radio observations. Recent monographs have been presented Equation (1 1. 1)are referred to as equivalent blackbody tem- by Kruger [1979] and Kundu and Gergely [1980]. perature or as brightness temperature defined as the tem- In Chapter I the basic phenomenological aspects of the perature of a blackbody that would produce the observed sun, its active regions, and solar flares are presented. This radiance at the specified frequency. chapter will focus on the three components of solar radio The radiant power received per unit area in a given emission: the basic (or minimum) component, the slowly frequency band is called the power flux density (irradiance varying component from active regions, and the transient per bandwidth) and is strictly defined as the integral of Bf,d component from flare bursts. between the limits f and f + Af, where Qs is the solid angle Different regions of the sun are observed at different subtended by the source.
    [Show full text]
  • HST/STIS Analysis of the First Main Sequence Pulsar CU Virginis
    A&A 625, A34 (2019) Astronomy https://doi.org/10.1051/0004-6361/201834937 & © ESO 2019 Astrophysics HST/STIS analysis of the first main sequence pulsar CU Virginis?,?? J. Krtickaˇ 1, Z. Mikulášek1, G. W. Henry2, J. Janík1, O. Kochukhov3, A. Pigulski4, P. Leto5, C. Trigilio5, I. Krtickovᡠ1, T. Lüftinger6, M. Prvák1, and A. Tichý1 1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlárskᡠ2, 611 37 Brno, Czech Republic e-mail: [email protected] 2 Center of Excellence in Information Systems, Tennessee State University, Nashville, TN, USA 3 Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden 4 Astronomical Institute, Wrocław University, Kopernika 11, 51-622 Wrocław, Poland 5 INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy 6 Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria Received 20 December 2018 / Accepted 5 March 2019 ABSTRACT Context. CU Vir has been the first main sequence star that showed regular radio pulses that persist for decades, resembling the radio lighthouse of pulsars and interpreted as auroral radio emission similar to that found in planets. The star belongs to a rare group of magnetic chemically peculiar stars with variable rotational period. Aims. We study the ultraviolet (UV) spectrum of CU Vir obtained using STIS spectrograph onboard the Hubble Space Telescope (HST) to search for the source of radio emission and to test the model of the rotational period evolution. Methods. We used our own far-UV and visual photometric observations supplemented with the archival data to improve the parameters of the quasisinusoidal long-term variations of the rotational period.
    [Show full text]
  • Young Stellar Object Candidates Toward the Orion Region Selected from GALEX (Research Note)
    A&A 572, A89 (2014) Astronomy DOI: 10.1051/0004-6361/201424629 & c ESO 2014 Astrophysics Young stellar object candidates toward the Orion region selected from GALEX (Research Note) Nestor Sanchez, Ana Inés Gómez de Castro, Fátima Lopez-Martinez, and Javier López-Santiago S. D. Astronomía y Geodesia, Fac. CC. Matemáticas, Universidad Complutense de Madrid, 28040 Madrid, Spain e-mail: [email protected] Received 18 July 2014 / Accepted 28 October 2014 ABSTRACT We analyze 359 ultraviolet tiles from the All Sky Imaging Survey of the space mission GALEX covering roughly 400 square degrees toward the Orion star-forming region. There are a total of 1 555 174 ultraviolet sources that were cross-matched with other catalogs (2MASS, UCAC4, SDSS, DENIS, CMC15, and WISE) to produce a list of 290 717 reliable sources with a wide range of photometric information. Using different color selection criteria, we identify 111 young stellar object candidates showing both ultraviolet and infrared excesses, of which 81 are new identifications. We discuss the spatial distribution, the spectral energy distributions, and other physical properties of these stars. Their properties are, in general, compatible with those expected for T Tauri stars. This population of TTS candidates is widely dispersed around the Orion molecular cloud. Key words. stars: low-mass – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be – ultraviolet: stars 1. Introduction and magnetic stellar activity (Edwards et al. 1994; Muzerolle et al. 1998). As spectroscopic observations are time consuming The current paradigm for low-mass star formation catego- and are sometimes restricted to bright objects, a good strategy is rizes young stellar objects (YSOs) into four general classes: to perform spectroscopic follow-ups only for the most reliable Class 0 sources are faint central protostars surrounded by a YSO candidates selected using photometric methods.
    [Show full text]
  • PS 224, Fall 2014 HW 4
    PS 224, Fall 2014 HW 4 1. True or False? Explain in one or two short sentences. a. Scientists are currently building an infrared telescope designed to observe fusion reactions in the Sun’s core. False. Infrared telescopes cannot see through the Sun. b. Two stars that look very different must be made of different kinds of elements. False. What a star looks like depends on many different properties like mass, age, and size. c. Two stars that have the same apparent brightness in the sky must also have the same luminosity. False. How bright a star appears depends on the luminosity of a stars and its distance away from us. d. Some of the stars on the main sequence of the H-R diagram are not converting hydrogen into helium. False. The main-seuqence is defined as the phase of a star’s life when it burns hydrogen into helium. e. Stars that begin their lives with the most mass live longer than less massive stars because they have so much more hydrogen fuel. False. Massive stars live have shorter lifetimes as they burn through their fuel faster. f. All giants, supergiants, and white dwarfs were once main-sequence stars. True. Main-sequence stars evolve to become giants and supergiants based on their mass and eventually end up as white dwarfs. g. The iron in my blood came from a star that blew up more than 4 billion years ago. True. All elements except hydrogen and helium were produced in stars. h. If the Sun had been born 4½ billion years ago as a high-mass star rather than as a low- mass star, Jupiter would have Earth-like conditions today, while Earth would be hot like Venus.
    [Show full text]